It is a naturally constant endeavor to optimize the operation of a high pressure pump, which may be done for example by diagnosis of failing and/or limited performance of any part of the high pressure pump for operation of the high pressure pump, while taking this into consideration for optimal use of the high pressure pump or fixing of degraded parts of the maintenance or replacement. Thus, limited performance ability of the high pressure pump may be due to the occurrence of a leakage in one or several of the pump elements between the inlet valve and the pump chamber's connecting opening to the low pressure part, e.g. because of a somewhat damaged valve, or leakage between the piston and the pump chamber wall because of wear particles having got caught in the fuel and damaging the wall.
U.S. Pat. No. 6,526,948 B1 describes a method which facilitates a determination, through pressure measurements, of whether a pump element, or the entire high pressure pump in a system for fuel injection in a combustion engine, has failed.